Electroless copper plating compositions and methods for electroless plating copper on substrates

ABSTRACT

Stable electroless copper plating baths include pyridinium compounds to improve rate of copper deposition on substrates. The copper from the electroless plating baths can be plated at low temperatures and at high plating rates.

FIELD OF THE INVENTION

The present invention is directed to electroless copper platingcompositions and methods for electroless plating copper on substrates,wherein electroless copper plating has a high electroless copper platingrate at low temperatures and the electroless copper plating compositionsare stable. More specifically, the present invention is directed toelectroless copper plating compositions and methods for electrolessplating copper on substrates, wherein electroless copper plating has ahigh electroless copper plating rate at low temperatures and theelectroless copper plating compositions are stable, wherein theelectroless copper plating compositions include pyridinium compounds orsalts thereof.

BACKGROUND OF THE INVENTION

Electroless copper plating baths are in widespread use in metallizationindustries for depositing copper on various types of substrates. In themanufacture of printed circuit boards, for example, the electrolesscopper baths are used to deposit copper on walls of through-holes andcircuit paths as a base for subsequent electrolytic copper plating.Electroless copper plating also is used in the decorative plasticsindustry for deposition of copper on non-conductive surfaces as a basefor further plating of copper, nickel, gold, silver and other metals, asrequired. Electroless copper baths which are in commercial use todaycontain water soluble divalent copper compounds, chelating agents orcomplexing agents, for example, Rochelle salts and sodium salts ofethylenediamine tetraacetic acid, for chelating the divalent copperions, reducing agents, for example, formaldehyde, and formaldehydeprecursors or derivatives, and various addition agents to make the bathmore stable, adjust the plating rate and brighten the copper deposit.

It should be understood, however, that every component in theelectroless copper bath has an effect on plating potential, andtherefore, must be regulated in concentration to maintain the mostdesirable plating potential for particular ingredients and conditions ofoperation. Other factors which affect internal plating voltage,deposition quality and rate include temperature, degree of agitation,type and concentration of basic ingredients mentioned above.

In electroless copper plating baths, the components are continuouslyconsumed such that the baths are in a constant state of change, thusconsumed components must be periodically replenished. Control of thebaths to maintain high plating rates with substantially uniform copperdeposits over long periods of time is exceedingly difficult. In general,electroless copper plating rates of equal to or greater than 0.6 μm/5min. are highly desirable (preferably desired for current horizontalplating applications) but rarely achieved, especially at low electrolessplating temperatures, such as below 40° C. Consumption and replenishmentof bath components over several metal turnovers (MTO) can alsocontribute to bath instability, for example, through the buildup of sideproducts. Therefore, such baths, and particularly those having a highplating potential, i.e. highly active baths, tend to become unstable andto spontaneously decompose with use. Such electroless copper bathinstability can result in non-uniform or discontinuous copper platingalong a surface. For example, in the manufacture of printed circuitboards, it is important to plate electroless copper on the walls ofthrough-holes such that the copper deposit on the walls is substantiallycontinuous and uniform with minimal, preferably, no break or gaps in thecopper deposit. Such discontinuity of the copper deposit can ultimatelylead to mal-functioning of any electrical device in which the defectiveprinted circuit board is included.

To address the foregoing stability issues, various chemical compoundscategorized under the label “stabilizers” have been introduced toelectroless copper plating baths. Examples of stabilizers which havebeen used in electroless copper plating baths are sulfur containingcompounds, such as disulfides and thiols. However, many stabilizerslower electroless copper plating rates, and, also, at highconcentrations can be catalyst poisons, thus reducing plating rates orinhibiting plating and compromising the performance of the plating bath.Low plating rates are detrimental to electroless copper platingperformance. Electroless copper plating rate is also temperaturedependent, thus when high stabilizer concentrations lower the rate,increasing the plating temperature can increase the rate. However,increasing the operating temperatures can decrease the stability of theelectroless copper bath by increasing the buildup of byproducts as wellas increasing the rate of generation of byproducts by side reactions,thus negating some of the effects of increasing the stabilizerconcentration. As a result, in most cases the amount of stabilizer usedmust be a careful compromise between maintaining a high plating rate andachieving an electroless bath that is stable over a long period of time.

Alternatively, an “accelerator” additive can be incorporated into theelectroless bath formulation. Ideally, the accelerator additive does notimpact the stability of the electroless bath, such that higher platingrates can be achieved while keeping bath stability in check; or suchthat the same plating rate is now achieved at lower temperatures whichtypically also results in a more stable bath. The lower electroless bathtemperatures reduce cost of the electroless bath, for example, bydecreasing the rate of passive consumption of plating chemicals.Furthermore, a more stable formulation, which is afforded by loweringthe working temperature, results in lower maintenance requirements.Finally, lower plating temperatures can lower the build-up of internalstress in the electroless deposit, making the metallization processbetter suited for high-adhesion applications. Thus, rate acceleration inelectroless copper plating is a key strategy for lowering workingtemperatures, lowering internal stress of copper deposits such as onflexible substrates and decreasing overall running costs ofmetallization.

Therefore, there is a need for an additive for electroless copperplating baths which enables a high rate of electroless copper plating atlow temperatures to provide bright and uniform copper deposits onsubstrates.

SUMMARY OF THE INVENTION

The present invention is directed to an electroless copper platingcomposition including one or more sources of copper ions, one or morepyridinium compounds, one or more complexing agents, one or morereducing agents, and, optionally, one or more pH adjusting agents,wherein a pH of the electroless copper plating composition is greaterthan 7.

The present invention is also directed to a method of electroless copperplating including:

-   -   a) providing a substrate comprising a dielectric;    -   b) applying a catalyst to the substrate comprising the        dielectric;    -   c) applying an electroless copper plating composition to the        substrate comprising the dielectric, wherein the electroless        copper plating composition comprises one or more sources of        copper ions, one or more pyridinium compounds, one or more        complexing agents, one or more reducing agents, and, optionally,        one or more pH adjusting agents, wherein a pH of the electroless        copper plating composition is greater than 7; and    -   d) electroless plating copper on the substrate comprising the        dielectric with the electroless copper plating composition.

The pyridinium compounds enable increased electroless copper platingrates at low plating temperatures of less than or equal to 40° C. Theelectroless copper plating compositions and methods of the presentinvention further enable good through-hole wall coverage, even at lowplating temperatures. Low plating temperatures reduce consumption ofelectroless copper plating composition additives which occur byundesired side reactions or by decomposition, thus providing a morestable electroless copper plating composition, and lower the cost ofoperating the electroless copper plating process.

The electroless copper plating compositions of the present invention arestable over wide concentration ranges of the pyridinium compounds. Abroad operating window for the pyridinium compounds concentration meansthat the pyridinium compounds concentrations do not need to be carefullymonitored such that the performance of the electroless copper platingcompositions do not substantially change regardless of how thecomposition components are being replenished and consumed.

DETAILED DESCRIPTION OF THE INVENTION

As used throughout this specification, the abbreviations given belowhave the following meanings, unless the context clearly indicatesotherwise: g=gram; mg=milligram; mL=milliliter; L=liter; cm=centimeter;mm=millimeter; μm=micron; ppm=parts per million=mg/L; ° C.=degreesCentigrade; g/L=grams per liter; DI=deionized; C=the element carbon;Pd=palladium; Pd(II)=palladium ions with a +2 oxidation state;Pd°=palladium reduced to its metal state vs. its ionic state; wt%=percent by weight; and T_(g)=glass transition temperature.

All amounts are percent by weight, unless otherwise noted. All numericalranges are inclusive and combinable in any order except where it islogical that such numerical ranges are constrained to add up to 100%.

The terms “plating” and “deposition” are used interchangeably throughoutthis specification. The terms “composition” and “bath” are usedinterchangeably throughout this specification. The term “alkyl”, unlessotherwise described in the specification as having substituent groups,means an organic chemical group composed of only carbon and hydrogen andhaving a general formula: C_(n)H_(2n+1). The term “average” isequivalent to the mean value of a sample. All amounts are percent byweight, unless otherwise noted. All numerical ranges are inclusive andcombinable in any order except where it is logical that such numericalranges are constrained to add up to 100%.

The electroless copper plating compositions of the present inventioninclude one or more sources of copper ions, one or more pyridiniumcompounds, one or more complexing agents; one or more reducing agents;water; and, optionally, one or more pH adjusting agents, wherein a pH ofthe electroless copper plating composition is greater than 7.

Preferably, the one or more pyridinium compounds have a formula:

wherein R₁ is selected from the group consisting of linear or branched,substituted or unsubstituted (C₁-C₁₀)alkyl, substituted or unsubstituted(C₆-C₁₀)aryl, substituted or unsubstituted (C₆-C₁₀) heterocyclicaromatic groups and substituted or unsubstituted benzyl, whereinsubstituent groups are selected from the group consisting of hydroxyl,sulfate, amino, amide, carbonyl and carboxyl; and R₂ is selected fromthe group consisting of hydrogen, hydroxyl, sulfate, carbonyl, carboxyl,vinyl, amino and amide. More preferably, R₁ is selected from the groupconsisting of linear or branched, substituted and unsubstituted(C₂-C₄)alkyl and substituted or unsubstituted C₆-heterocyclic aromaticgroup, wherein the substituent groups are selected from the groupconsisting of hydroxyl and sulfate; and, more preferably, R₂ is selectedfrom the group consisting of hydrogen, hydroxyl and sulfate; and, mostpreferably, R₁ is selected from the groups consisting of linear,substituted or unsubstituted (C₂-C₄)alkyl, wherein a preferredsubstituent is sulfate; and, most preferably, R₂ is hydrogen.Preferably, the pyridinium compound of formula (I) includes a counteranion to neutralize the positive charge of the pyridinium compound.

Preferably, the foregoing pyridinium compounds are hydroxide salts,sulfate, tetrafluoroborate, hexafluorophosphate, nitrate, formate,acetate, tartrate or halogen salts, wherein the halogen is selected fromthe group consisting of chloride, bromide, fluoride and iodide. Morepreferably, the salts are halogens selected from the group consisting ofchloride and bromide, most preferably, the halogen is chloride. Examplesof three preferred pyridinium compounds of the present invention are thesalts 1-butylpyridinium chloride, and 1-(3-sulfopropyl) pyridiniumhydroxide inner salt (also known as 1-(3-sulfopropyl) pyridinium) and1-(4-pyridyl) pyridinium chloride.

The pyridinium compounds of the present invention are included inamounts of 0.5 ppm or greater, preferably, from 1 ppm to 50 ppm, morepreferably, from 2 ppm to 30 ppm, even more preferably, from 2.5 ppm to20 ppm, most preferably, from 5 ppm to 20 ppm.

Sources of copper ions and counter anions include, but are not limitedto, water soluble halides, nitrates, acetates, sulfates and otherorganic and inorganic salts of copper. Mixtures of one or more of suchcopper salts can be used to provide copper ions. Examples are coppersulfate, such as copper sulfate pentahydrate, copper chloride, coppernitrate, copper hydroxide and copper sulfamate. Preferably, the one ormore sources of copper ions in the electroless copper platingcomposition of the present invention range from 0.5 g/L to 30 g/L, morepreferably, from 1 g/L to 25 g/L, even more preferably, from 5 g/L to 20g/L, further preferably, from 5 g/L to 15 g/L, and most preferably, from10 g/L to 15 g/L.

Complexing agents include, but are not limited to, sodium potassiumtartrate, sodium tartrate, sodium salicylate, sodium salts ofethylenediamine tetraacetic acid (EDTA), nitriloacetic acid and itsalkali metal salts, gluconic acid, gluconates, triethanolamine, modifiedethylene diamine tetraacetic acids, S,S-ethylene diamine disuccinicacid, hydantoin and hydantoin derivatives. Hydantoin derivativesinclude, but are not limited to, 1-methylhydantoin,1,3-dimethylhydantoin and 5,5-dimethylhydantoin. Preferably, thecomplexing agents are chosen from one or more of sodium potassiumtartrate, sodium tartrate, nitriloacetic acid and its alkali metalsalts, such as sodium and potassium salts of nitirloacetic acid,hydantoin and hydantoin derivatives. Preferably, EDTA and its salts areexcluded from the electroless copper plating compositions of the presentinvention. More preferably, the complexing agents are chosen from sodiumpotassium tartrate, sodium tartrate, nitriloacetic acid, nitriloaceticacid sodium salt, and hydantoin derivates. Even more preferably, thecomplexing agents are chosen from sodium potassium tartrate, sodiumtartrate, 1-methylhydantoin, 1,3-dimethylhydantoin and5,5-dimethylhydantoin. Further preferably, the complexing agents arechosen from sodium potassium tartrate and sodium tartrate. Mostpreferably, the complexing agent is sodium potassium tartrate (Rochellesalts).

Complexing agents are included in the electroless copper platingcompositions of the present invention in amounts of 10 g/l to 150 g/L,preferably, from 20 g/L to 150 g/L, more preferably, from 30 g/L to 100g/L, even more preferably, from 35 g/L to 80 g/L, and, most preferably,from 35 g/l to 55 g/L.

Reducing agents include, but are not limited to, aldehydes, such as,formaldehyde, formaldehyde precursors, formaldehyde derivatives, such asparaformaldehyde, borohydrides, such sodium borohydride, substitutedborohydrides, boranes, such as dimethylamine borane (DMAB), saccharides,such as grape sugar (glucose), glucose, sorbitol, cellulose, cane sugar,mannitol and gluconolactone, hypophosphite and salts thereof, such assodium hypophosphite, hydroquinone, catechol, resorcinol, quinol,pyrogallol, hydroxyquinol, phloroglucinol, guaiacol, gallic acid,glyoxylic acid, 3,4-dihydroxybenzoic acid, phenolsulfonic acid,cresolsulfonic acid, hydroquinonsulfonic acid, catecholsulfonic acid,tiron and salts of all of the foregoing reducing agents. Preferably, thereducing agents are chosen from formaldehyde, formaldehyde derivatives,formaldehyde precursors, borohydrides and hypophosphite and saltsthereof, hydroquinone, catechol, resorcinol, and gallic acid. Morepreferably, the reducing agents are chosen from formaldehyde,formaldehyde derivatives, formaldehyde precursors, and sodiumhypophosphite. Most preferably, the reducing agent is formaldehyde.

Reducing agents are included in the electroless copper platingcompositions of the present invention in amounts of 0.5 g/L to 100 g/L,preferably, from 0.5 g/L to 60 g/L, more preferably, from 1 g/L to 50g/L, even more preferably, from 1 g/L to 20 g/L, further preferably,from 1 g/L to 10 g/L, most preferably, from 1 g/L to 5 g/L.

A pH of the electroless copper plating composition of the presentinvention is greater than 7. Preferably, the pH of the electrolesscopper plating compositions of the present invention is greater than7.5. More preferably, the pH of the electroless copper platingcompositions range from 8 to 14, even more preferably, from 10 to 14,further preferably, from 11 to 13, and most preferably, from 12 to 13.

Optionally, but preferably, one or more pH adjusting agents can beincluded in the electroless copper plating compositions of the presentinvention to adjust the pH of the electroless copper platingcompositions to an alkaline pH. Acids and bases can be used to adjustthe pH, including organic and inorganic acids and bases. Preferably,inorganic acids or inorganic bases, or mixtures thereof are used toadjust the pH of the electroless copper plating compositions of thepresent invention. Inorganic acids suitable for use of adjusting the pHof the electroless copper plating compositions include, for example,phosphoric acid, nitric acid, sulfuric acid and hydrochloric acid.Inorganic bases suitable for use of adjusting the pH of the electrolesscopper plating compositions include, for example, ammonium hydroxide,sodium hydroxide, potassium hydroxide and lithium hyddroxide.Preferably, sodium hydroxide, potassium hydroxide or mixtures thereofare used to adjust the pH of the electroless copper platingcompositions, most preferably, sodium hydroxide is used to adjust the pHof the electroless copper plating compositions of the present invention.

Optionally, but preferably, one or more stabilizers can be included inthe electroless copper plating compositions of the present invention.Stabilizers include, but are not limited to 2,2′-dipyridyl andderivatives, 4,4′-dipyridyl, phenanthroline and phenanthrolinederivatives, thiomalic acid, 2,2′ dithiodisuccinic acid,mercaptosuccinic acid, cysteine, methionine, thionine, thiourea,benzothiazole, mercaptobenzothiazole, 2,2′-thiodiacetic acid,3,3′-thiodipropionic acid, 3,3′-dithiodipropionic acid, thiosulfate, andglycols such as polypropylene glycol and polyethylene glycol.

Such optional stabilizers are included in the electroless copper platingcompositions of the present invention in amounts of 0.1 ppm to 20 ppm,preferably, from 0.5 ppm to 10 ppm, more preferably, from 0.5 ppm to 5ppm, most preferably from 0.5 ppm to 2 ppm.

Optionally, but preferably, one or more secondary accelerators can beincluded in the electroless copper plating compositions of the presentinvention. Such accelerators include, but are not limited to, severalfree nitrogen bases such as guanidine, guanidine derivatives, such asguanidine hydrochloride, pyridine and pyridine derivatives such asaminopyridine, di- and trialkylamines, such as trimethylamine andtriethylamine, N,N,N′,N′-Tetrakis(2-Hydroxypropyl)ethylenediamine, andethylenediaminetetraacetic acid, and nickel(II) salts such as Nickel(II)sulfate. An example of a preferred secondary accelerator is guanidinehydrochloride.

Such accelerators can be included in amounts of 0.1 ppm to 500 ppm,preferably, from 0.2 to 15 ppm, more preferably from, 0.3 ppm to 10 ppm,most preferably from 0.3 ppm to 5 ppm.

Optionally, one or more surfactants can be included in the electrolesscopper plating compositions of the present invention. Such surfactantsinclude ionic, such as cationic and anionic surfactants, non-ionic andamphoteric surfactants. Mixtures of the surfactants can be used.Surfactants can be included in the compositions in amounts of 0.001 g/Lto 50 g/L, preferably in amounts of 0.01 g/L to 50 g/L.

Cationic surfactants include, but are not limited to,tetra-alkylammonium halides, alkyltrimethylammonium halides,hydroxyethyl alkyl imidazoline, alkyl imidazolium, alkylbenzalkoniumhalides, alkylamine acetates, alkylamine oleates and alkylaminoethylglycine.

Anionic surfactants include, but are not limited to,alkylbenzenesulfonates, alkyl or alkoxy naphthalene sulfonates,alkyldiphenyl ether sulfonates, alkyl ether sulfonates, alkylsulfuricesters, polyoxyethylene alkyl ether sulfuric esters, polyoxyethylenealkyl phenol ether sulfuric esters, higher alcohol phosphoricmonoesters, polyoxyalkylene alkyl ether phosphoric acids (phosphates)and alkyl sulfosuccinates.

Amphoteric surfactants include, but are not limited to,2-alkyl-N-carboxymethyl or ethyl-N-hydroxyethyl or methyl imidazoliumbetaines, 2-alkyl-N-carboxymethyl or ethyl-N-carboxymethyloxyethylimidazolium betaines, dimethylalkyl betains, N-alkyl-β-aminopropionicacids or salts thereof and fatty acid amidopropyl dimethylaminoaceticacid betaines.

Preferably, the surfactants are non-ionic. Non-ionic surfactantsinclude, but are not limited to, alkyl phenoxy polyethoxyethanols,polyoxyethylene polymers having from 20 to 150 repeating units andrandom and block copolymers of polyoxyethylene and polyoxypropylene, andpolyamines, such as polyallylamine.

Optionally, one or more grain refiner can be included in the electrolesscopper plating compositions of the present invention. Grain refinersinclude, but are not limited to, cyanide and cyanide containinginorganic salts such as potassium hexacyanoferrate,2-mercaptobenthiazole, 2,2′-bipyridine and 2,2′-bipyridine derivatives,1,10-phenanthroline and 1,10-phenanthroline derivatives, vanadium oxidessuch as sodium Metavanadate, and nickel salts such as nickel(II)sulfate. Grain refiners are included in amounts well known to those ofordinary skill in the art.

Preferably, the electroless copper plating composition of the presentinvention consists of one or more sources of copper ions, includingcorresponding anions, one or more pyridinium compounds or salts thereofhaving formula (I), one or more complexing agents, one or more reducingagents, water, optionally, one or more pH adjusting agents, optionally,one or more stabilizers, optionally, one or more secondary accelerators,optionally, one or more surfactants, and optionally, one or more grainrefiners, wherein a pH of the electroless copper plating composition is10-14.

More preferably, the electroless copper plating composition of thepresent invention consists of one or more sources of copper ions,including corresponding anions, one or more pyridinium compounds orsalts thereof having formula (I), wherein the salts are selected fromthe group consisting of hydroxide, chloride and bromide salts, one ormore complexing agents, one or more reducing agents, water, one or morepH adjusting agents, one or more stabilizers, optionally, one or moresecondary accelerators, optionally, one or more surfactants, and,optionally, one or more grain refiners, wherein a pH of the electrolesscopper plating composition is 11-13.

Most preferably, the electroless copper plating compositions of thepresent invention consist of one or more sources of copper ions,including corresponding anions, one or more pyridinium compoundsselected from the group consisting of 1-butyl pyridinium chloride,1-(3-sulfopropyl) pyridinium hydroxide and 1-(4-pyridyl) pyridiniumchloride, one or more complexing agents, one or more reducing agents,water, one or more pH adjusting agents, one or more stabilizers,optionally, one or more secondary accelerators, optionally, one or moresurfactants, and, optionally, one or more grain refiners, wherein a pHof the electroless copper plating composition is 12-13.

The electroless copper compositions and methods of the present inventioncan be used to electroless plate copper on various substrates such asdielectrics, semiconductors, metal-clad and unclad substrates such asprinted circuit boards. Such metal-clad and unclad printed circuitboards can include thermosetting resins, thermoplastic resins andcombinations thereof, including fibers, such as fiberglass, impregnatedembodiments of the foregoing. Preferably the substrate is a metal-cladprinted circuit or wiring board with a plurality of through-holes, vias,or combinations thereof. The electroless copper plating compositions andmethods of the present invention can be used in both horizontal andvertical processes of manufacturing printed circuit boards, preferably,the electroless copper plating compositions methods of the presentinvention are used in horizontal processes.

Thermoplastic resins include, but are not limited to, acetal resins,acrylics, such as methyl acrylate, cellulosic resins, such as ethylacetate, cellulose propionate, cellulose acetate butyrate and cellulosenitrate, polyethers, nylon, polyethylene, polystyrene, styrene blends,such as acrylonitrile styrene and copolymers and acrylonitrile-butadienestyrene copolymers, polycarbonates, polychlorotrifluoroethylene, andvinylpolymers and copolymers, such as vinyl acetate, vinyl alcohol,vinyl butyral, vinyl chloride, vinyl chloride-acetate copolymer,vinylidene chloride and vinyl formal.

Thermosetting resins include, but are not limited to allyl phthalate,furane, melamine-formaldehyde, phenol-formaldehyde and phenol-furfuralcopolymers, alone or compounded with butadiene acrylonitrile copolymersor acrylonitrile-butadiene-styrene copolymers, polyacrylic esters,silicones, urea formaldehydes, epoxy resins, allyl resins, glycerylphthalates, and polyesters.

The electroless copper plating compositions and methods of the presentinvention can be used to electroless copper plate substrates with bothlow and high T_(g) resins. Low T_(g) resins have a T_(g) below 160° C.and high T_(g) resins have a T_(g) of 160° C. and above. Typically, highT_(g) resins have a T_(g) of 160° C. to 280° C. or such as from 170° C.to 240° C. High T_(g) polymer resins include, but are not limited to,polytetrafluoroethylene (PTFE) and polytetrafluoroethylene blends. Suchblends include, for example, PTFE with polyphenylene oxides and cyanateesters. Other classes of polymer resins which include resins with a highT_(g) include, but are not limited to, epoxy resins, such asdifunctional and multifunctional epoxy resins, bimaleimide/triazine andepoxy resins (BT epoxy), epoxy/polyphenylene oxide resins, acrylonitrilebutadienestyrene, polycarbonates (PC), polyphenylene oxides (PPO),polypheneylene ethers (PPE), polyphenylene sulfides (PPS), polysulfones(PS), polyamides, polyesters such as polyethyleneterephthalate (PET) andpolybutyleneterephthalate (PBT), polyetherketones (PEEK), liquid crystalpolymers, polyurethanes, polyetherimides, epoxies and compositesthereof.

In the method of electroless copper plating with the electroless coppercompositions of the present invention, optionally, the substrates arecleaned or degreased, optionally, roughened or micro-roughened,optionally, the substrates are etched or micro-etched, optionally, asolvent swell is applied to the substrates, through-holes are desmeared,and various rinse and anti-tarnish treatments can, optionally, be used.

Preferably, the substrates to be electroless copper plated with theelectroless copper plating compositions and methods of the presentinvention are metal-clad substrates with dielectric material and aplurality of through-holes such as printed circuit boards. Optionally,the boards are rinsed with water and cleaned and degreased followed bydesmearing the through-hole walls. Prepping or softening the dielectricor desmearing of the through-holes can begin with application of asolvent swell. Although, it is preferred, that the method of electrolesscopper plating is for plating through-hole walls, it is envisioned thatthe method of electroless copper plating can also be used to electrolesscopper plate walls of vias.

Conventional solvent swells can be used. The specific type can varydepending on the type of dielectric material. Minor experimentation canbe done to determine which solvent swell is suitable for a particulardielectric material. The T_(g) of the dielectric often determines thetype of solvent swell to be used. Solvent swells include, but are notlimited to, glycol ethers and their associated ether acetates.Conventional amounts of glycol ethers and their associated etheracetates well known to those of skill in the art can be used. Examplesof commercially available solvent swells are CIRCUPOSIT™ Conditioner3302A, CIRCUPOSIT™ Hole Prep 3303 and CIRCUPOSIT™ Hole Prep 4120solutions (available from Dow Electronic Materials).

After the solvent swell, optionally, a promoter can be applied.Conventional promoters can be used. Such promoters include sulfuricacid, chromic acid, alkaline permanganate or plasma etching. Preferably,alkaline permanganate is used as the promoter. Examples of commerciallyavailable promoters are CIRCUPOSIT™ Promoter 4130 and CIRCUPOSIT™ MLBPromoter 3308 solutions (available from Dow Electronic Materials).Optionally, the substrate and through-holes are rinsed with water.

If a promoter is used, a neutralizer is then applied to neutralize anyresidues left by the promoter. Conventional neutralizers can be used.Preferably, the neutralizer is an aqueous acidic solution containing oneor more amines or a solution of 3 wt % hydrogen peroxide and 3 wt %sulfuric acid. An example of a commercially available neutralizer isCIRCUPOSIT™ MLB Neutralizer 216-5. Optionally, the substrate andthrough-holes are rinsed with water and then dried.

After neutralizing an acid or alkaline conditioner is applied.Conventional conditioners can be used. Such conditioners can include oneor more cationic surfactants, non-ionic surfactants, complexing agentsand pH adjusters or buffers. Examples of commercially available acidconditioners are CIRCUPOSIT™ Conditioners 3320A and 3327 solutions(available from Dow Advanced Materials). Suitable alkaline conditionersinclude, but are not limited to, aqueous alkaline surfactant solutionscontaining one or more quaternary amines and polyamines. Examples ofcommercially available alkaline surfactants are CIRCUPOSIT™ Conditioner231, 3325, 813 and 860 formulations (available from Dow ElectronicMaterials). Optionally, the substrate and through-holes are rinsed withwater.

Optionally, conditioning can be followed by micro-etching. Conventionalmicro-etching compositions can be used. Micro-etching is designed toclean and provide a micro-roughened metal surface on exposed metal (e.g.innerlayers and surface etch) to enhance subsequent adhesion of platedelectroless copper and later electroplate. Micro-etches include, but arenot limited to, 60 g/L to 120 g/L sodium persulfate or sodium orpotassium oxymonopersulfate and sulfuric acid (2%) mixture, or genericsulfuric acid/hydrogen peroxide. Examples of commercially availablemicro-etching compositions are CIRCUPOSIT™ Microetch 3330 Etch solutionand PREPOSIT™ 748 Etch solution (both available from Dow ElectronicMaterials). Optionally, the substrate is rinsed with water.

Optionally, a pre-dip can then be applied to the micro-etched substrateand through-holes. Examples of pre-dips include, but are not limited to,organic salts such as sodium potassium tartrate or sodium citrate, 0.5%to 3% sulfuric acid, nitric acid, or an acidic solution of 25 g/L to 75g/L sodium chloride. An example of a commercially available pre-dip isacidic Pre-Dip CIRCUPOSIT™ 6520 solution.

A catalyst is then applied to the substrate. While it is envisioned thatany conventional catalyst suitable for electroless metal plating whichincludes a catalytic metal can be used, preferably, a palladium catalystis used in the methods of the present invention. The catalyst can be anon-ionic palladium catalyst, such as a colloidal palladium-tincatalyst, or the catalyst can be an ionic palladium. If the catalyst isa colloidal palladium-tin catalyst, an acceleration step is done tostrip tin from the catalyst and to expose the palladium metal forelectroless copper plating. If the catalyst is a colloidal palladium-tincatalyst, an acceleration step is applied after catalyst adsorption, forexample, by using hydrochloric acid, sulfuric acid or tetrafluoroboricacid as the accelerator at 0.5-10% in water to strip tin from thecatalyst and to expose the palladium metal for electroless copperplating. If the catalyst is an ionic catalyst, the acceleration step isexcluded from the method and, instead, a reducing agent is applied tothe substrate subsequent to application of the ionic catalyst to reducethe metal ions of the ionic catalyst to their metallic state, such as Pd(II) ions to Pd° metal. Examples of suitable commercially availablecolloidal palladium-tin catalysts are CIRCUPOSIT™ 3340 catalyst andCATAPOSIT™ 44 catalyst (available from Dow Electronic Materials). Anexample of a commercially available palladium ionic catalyst isCIRCUPOSIT™ 6530 Catalyst. The catalyst can be applied by immersing thesubstrate in a solution of the catalyst, or by spraying the catalystsolution on the substrate, or by atomization of the catalyst solution onthe substrate using conventional apparatus. The catalysts can be appliedat temperatures from room temperature to 80° C., preferably, from 30° C.to 60° C. The substrate and through-holes are optionally rinsed withwater after application of the catalyst.

Conventional reducing agents known to reduce metal ions to metal can beused to reduce the metal ions of the catalysts to their metallic state.Such reducing agents include, but are not limited to, dimethylamineborane (DMAB), sodium borohydride, ascorbic acid, iso-ascorbic acid,sodium hypophosphite, hydrazine hydrate, formic acid and formaldehyde.Reducing agents are included in amounts to reduce substantially all ofthe metal ions to metal. Such amounts are well known by those of skillin the art. If the catalyst is an ionic catalyst, the reducing agentsare applied subsequent to the catalyst being applied to the substrateand prior to metallization.

The substrate and walls of the through-holes are then plated with copperusing an electroless copper plating composition of the presentinvention. Methods of electroless copper plating of the presentinvention can be done at temperatures of 40° C. or less. Preferably,methods of electroless copper plating of the present invention are doneat temperatures from room temperature to 40° C., more preferably,electroless copper plating is done from room temperature to 35° C., evenmore preferably, from 30° C. to 35° C., most preferably, from 30° C. to34° C. The substrate can be immersed in the electroless copper platingcomposition of the present invention or the electroless copper platingcomposition can be sprayed on the substrate. Methods of electrolesscopper plating of the present invention using electroless copper platingcompositions of the present invention are done in an alkalineenvironment of pH greater than 7. Preferably, methods of electrolesscopper plating of the present invention are done at a pH of greater than7.5, more preferably, electroless copper plating is done at a pH of 8 to14, even more preferably, from 10 to 14, further preferably, from 11 to13, and most preferably, from 12 to 13.

Preferably, the electroless copper plating rates of the presentinvention are equal to or greater than 0.6 μm/5 min. at temperatures ofless than or equal to 40° C., more preferably, the electroless copperplating rates of the present invention are equal to or greater than 0.65μm/5 min., such as from 0.65 μm/5 min. to 1 μm/5 min., even morepreferably, equal to or greater than 0.7 μm/5 min., such as from 0.75μm/5 min. to 1 μm/5 min., or such as from 0.75 μm/5 min. to 0.8 μm/5min., at temperatures of less than or equal to 35° C., most preferably,electroless plating is done at temperatures from 30° C. to 34° C.

The methods of electroless copper plating using the electroless copperplating compositions of the present invention enable good averagebacklight values for electroless copper plating of through-holes ofprinted circuit boards. Such average backlight values are preferablygreater than or equal to 4.5, more preferably from 4.6 to 5, even morepreferably from 4.7 to 5, most preferably from 4.8 to 5. Such highaverage backlight values enable the methods of electroless copperplating of the present invention using the electroless copper platingcompositions of the present invention to be used for commercialelectroless copper plating, wherein the printed circuit board industrysubstantially requires backlight values of 4.5 and greater. Theelectroless copper metal plating compositions and methods of the presentinvention enable uniform, bright copper deposits over broadconcentration ranges of pyridinium compounds or salts thereof, even athigh plating rates.

The following examples are not intended to limit the scope of theinvention but to further illustrate the invention.

Example 1 Electroless Copper Plating Rates of an Electroless CopperPlating Baths Containing Pyridinium Compounds

Ten (10) electroless copper plating baths are prepared. All ten bathsinclude the following components:

1. 10 g/L Copper sulfate pentahydrate

2. 40 g/L Rochelle salts

3. 8 g/L Sodium hydroxide

4. 4 g/L Formaldehyde

5. 0.5 ppm 2,2′-dithiodisuccinic acid

6. Water (balance)

The pH of each bath is 13. To nine (9) of the electroless platingcompositions one of the following pyridinium compounds is added in theamount specified in Table 1. Bath 10 is a control where no pyridiniumcompounded is added.

TABLE 1 1-(3-sulfopropyl) 1-butylpyridinium pyridinium 1-(4-pyridyl)Bath chloride hydroxide pyridinium chloride 1 2.5 ppm  — — 2 10 ppm — —3 20 ppm — — 4 — 2.5 ppm  — 5 — 10 ppm — 6 — 20 ppm — 7 — — 2.5 ppm  8 —— 10 ppm 9 — — 20 ppmEach bath is used to plate copper on bare epoxy substrates of NP140material (Nanya, Taiwan). Each epoxy substrate is first treatedaccording to the following process prior to electroless copper plating:

(1) Conditioner 231 applied for 1.5 min. at 40° C.;

(2) Rinse with DI water for 2 min. at room temperature;

(3) Nitric acid pre-dip, pH=2, for 0.5 min. at room temperature;

(4) Rinse with DI water for 2 min. at room temperature;

(5) 100 ppm of CIRCUPOSIT™ 6530 Catalyst for 1 min. at 40° C.;

(6) Rinse with DI water for 1 min. at room temperature;

(7) 5 g/L boric acid and 0.6 g/L dimethylamine borane aqueous solutionfor 1 min. at 32° C.; and,

(8) Rinse with DI water for 1 min. at room temperature.

Electroless copper plating is done at 34° C. for 5 minutes. The platingrate is determined by weighing each substrate using a conventionallaboratory analytical balance prior to electroless copper plating andthen weighing each substrate subsequent to plating. The difference inthe weight of each substrate is then used to calculate the depositthickness using the laminate surface area, which is 25 cm² and thedensity of the copper deposit, 8.92 g/cm³ and the value is converted toplating rate by dividing over the plating time length. The plating ratefor each bath is shown in Table 2.

TABLE 2 Bath Plating Rate 1 0.72 μm/5 min. 2 0.77 μm/5 min. 3 0.74 μm/5min. 4 0.75 μm/5 min. 5 0.67 μm/5 min. 6 0.61 μm/5 min. 7 0.69 μm/5 min.8 0.59 μm/5 min. 9 0.61 μm/5 min. 10 (Control) 0.49 μm/5 min.Including 1-butylpyridinium chloride, 1-(3-sulfopropyl) pyridiniumhydroxide or 1-(4-pyridyl) pyridinium chloride in the electroless copperplating bath increases plating rate. The copper deposits from the bathscontaining 1-butylpyridinium chloride and 1-(3-sulfopropyl) pyridiniumhydroxide appear bright and uniform over substantially all of the epoxysubstrates over the concentrations of 2.5 ppm, 10 ppm and 20 ppm. Thecopper deposits plated from the baths containing 1-(4-pyridyl)pyridinium chloride show bright and uniform areas with minor patches ofrough deposits. The copper deposit plated from the control bath showslarge areas of irregular, rough and dark deposits with minor regions ofbright deposits.

Example 2 (Comparative) Electroless Copper Plating Rates of anElectroless Copper Plating Baths Containing Pyridine (Free NitrogenBase)

Three (3) electroless copper plating baths are prepared. All three bathsinclude the following components:

1. 10 g/L Copper sulfate pentahydrate

2. 40 g/L Rochelle salts

3. 8 g/L Sodium hydroxide

4. 4 g/L Formaldehyde

5. 0.5 ppm 2,2′-dithiodisuccinic acid

6. Water (balance)

The pH of each bath is 13. Pyridine is added to the baths in amounts of2.5 ppm (Comparative Bath 1), 10 ppm (Comparative Bath 2) or 20 ppm(Comparative Bath 3).

Each bath is used to plate copper on epoxy substrates. The epoxysubstrates are treated as described in Example 1 in preparation forelectroless copper plating. Electroless copper plating is done at 34° C.for 5 minutes. The plating rate is then determined as described inExample 1. The plating rate for each bath is shown in Table 3.

TABLE 3 Comparative Bath Plating Rate 1 0.65 μm/5 min. 2 0.48 μm/5 min.3 0.42 μm/5 min.Although the plating rate of pyridine at 2.5 ppm is higher than in theControl in Example 1, at higher concentrations of 10 ppm and 20 ppm theplating rates decline to below the plating rate of the control. Theplating rate of pyridine is less than the Control electroless copperbath in Example 1. The copper deposits have a mixture of bright anduniform areas and rough and dull areas.

Example 3 Electroless Copper Plating Rates of an Electroless CopperPlating Baths Containing Pyridinium Compounds and GuanidineHydrochloride

Fourteen (14) electroless copper plating baths are prepared. Allfourteen baths include the following components:

1. 10 g/L Copper sulfate pentahydrate

2. 40 g/L Rochelle salts

3. 8 g/L Sodium hydroxide

4. 4 g/L Formaldehyde

5. 0.5 ppm 2,2′-dithiodisuccinic acid

6. 0.36 ppm Guanidine Hydrochloride

7. Water (balance)

The pH of each bath is 13. To thirteen (13) of the electroless platingcompositions one of the following pyridinium compounds is added in theamount specified in Table 4. Bath 24 is a control where no pyridiniumcompounded is added.

TABLE 4 1-(3-sulfopropyl) 1-butylpyridinium pyridinium 1-(4-pyridyl)Bath chloride hydroxide pyridinium chloride 11 2.5 ppm  — — 12  5 ppm —— 13 10 ppm — — 14 15 ppm — — 15 20 ppm — — 16 — 2.5 ppm  — 17 —  5 ppm— 18 — 10 ppm — 19 — 15 ppm — 20 — 20 ppm — 21 — — 2.5 ppm  22 — —  5ppm 23 — — 10 ppmEach bath is used to plate copper on bare epoxy substrates. Each epoxysubstrate is treated prior to electroless copper plating as described inExample 1. Electroless copper plating is done at 34° C. for 5 minutes.The plating rate is determined as described above in Example 1. Theplating rate for each bath is shown in Table 5.

TABLE 5 Bath Plating Rate 11 0.46 μm/5 min. 12 0.75 μm/5 min. 13 0.78μm/5 min. 14 0.74 μm/5 min. 15 0.83 μm/5 min. 16 0.69 μm/5 min. 17 0.65μm/5 min. 18 0.74 μm/5 min. 19 0.78 μm/5 min. 20 0.66 μm/5 min. 21 0.98μm/5 min. 22 0.67 μm/5 min. 23 0.81 μm/5 min. 24 (Control)  0.5 μm/5min.Including 1-butylpyridinium chloride, 1-(3-sulfopropyl) pyridiniumhydroxide or 1-(4-pyridyl) pyridinium chloride in the electroless copperplating bath increases plating rate over the control which includedguanidine hydrochloride. The copper deposits from the baths containing1-butylpyridinium chloride and 1-(3-sulfopropyl) pyridinium hydroxideappear bright and uniform over substantially all of the epoxysubstrates. The copper deposits plated from the baths containing1-(4-pyridyl) pyridinium chloride show bright and uniform areas withminor patches of rough deposits. The copper deposit plated from thecontrol bath shows minor regions of bright deposits intermingled withlarge areas of irregular and rough deposits.

Example 4 (Comparative) Electroless Copper Plating Rates of anElectroless Copper Plating Baths Containing Pyridine (Free NitrogenBase) and Guanidine Hydrochloride

Five (5) electroless copper plating baths are prepared. All five bathsinclude the following components:

1. 10 g/L Copper sulfate pentahydrate

2. 40 g/L Rochelle salts

3. 8 g/L Sodium hydroxide

4. 4 g/L Formaldehyde

5. 0.5 ppm 2,2′-dithiodisuccinic acid

6. 0.36 ppm Guanidine hydrochloride

7. Water (balance)

The pH of each bath is 13. Pyridine is added to the baths in amounts of2.5 ppm (Comparative Bath 4), 5 ppm (Comparative Bath 5), 10 ppm(Comparative Bath 6), 15 ppm (Comparative Bath 7) or 20 ppm (ComparativeBath 8).

Each bath is used to plate copper on epoxy substrates. The epoxysubstrates are treated as described in Example 1 prior to electrolesscopper plating. Electroless copper plating is done at 34° C. for 5minutes. The plating rate is determined as described above in Example 1.The plating rate for each bath is shown in Table 6.

TABLE 6 Comparative Bath Plating Rate 4 0.61 μm/5 min. 5 0.62 μm/5 min.6 0.57 μm/5 min. 7 0.52 μm/5 min. 8 0.48 μm/5 min.Even in combination with the accelerator guanidine hydrochloride, thehighest plating rates for the electroless copper baths containing thebase pyridine are just above 0.60 μm/5 min. In general, increasing theconcentration of pyridine in the electroless bath shows a tendencytoward a decrease in electroless copper plating rate. The copperdeposits have bright and uniform areas intermixed with rough and dullareas.

Example 5 Backlight Experiment with Aqueous Alkaline Electroless CooperCompositions of the Present Invention Containing Pyridinium Compounds

The following aqueous alkaline electroless copper compositions of theinvention are prepared having the components and amounts disclosed inTable 7 below.

TABLE 7 Component Bath 25 Bath 26 Copper sulfate pentahydrate 10 g/L 10g/L Rochelle salts 40 g/L 40 g/L Sodium hydroxide 8 g/L 8 g/LFormaldehyde 4 g/L 4 g/L 2,2′-Dithiosuccinic acid 0.5 ppm 0.5 ppmGuanidine hydrochloride 0.36 ppm 0.36 ppm 1-butylpyridinium chloride 10ppm — 1-(3-sulfopropyl) — 10 ppm pyridinium hydroxide Water To one literTo one literThe pH of the aqueous alkaline electroless copper compositions have apH=13 at room temperature as measured using a conventional pH meteravailable from Fisher Scientific.

Six (6) different FR/4 glass epoxy panels with a plurality ofthrough-holes are provided: TUC-662, SY-1141, IT-180, 370HR, EM825 andNPGN. The panels are eight-layer copper-clad panels. TUC-662 is obtainedfrom Taiwan Union Technology, and SY-1141 is obtained from Shengyi.IT-180 is obtained from ITEQ Corp., NPGN is obtained from NanYa and370HR from Isola and EM825 are obtained from Elite MaterialsCorporation. The T_(g) values of the panels range from 140° C. to 180°C. Each panel is 5 cm×10 cm.

The through-holes of each panel are treated as follows:

-   -   1. The through-holes of each panel are desmeared with        CIRCUPOSIT™ Hole Prep 3303 solution for 6 min. at 80° C.;    -   2. The through-holes of each panel are then rinsed with flowing        tap water for 2 min.;    -   3. The through-holes are then treated with CIRCUPOSIT™ MLB        Promoter 3308 aqueous permanganate solution at 80° C. for 8        min.;    -   4. The through-holes are then rinsed for 4 min. in flowing tap        water;    -   5. The through-holes are then treated with a 3 wt % sulfuric        acid/3 wt % hydrogen peroxide neutralizer at room temperature        for 2 min.;    -   6. The through-holes of each panel are then rinsed with flowing        tap water for 2 min.;    -   7. The through-holes of each panel are then treated with        CIRCUPOSIT™ Conditioner 231 alkaline solution for 1.5 min. at        60° C.;    -   8. The through-holes are then rinsed with flowing tap water for        2 min.;    -   9. The through-holes are then treated with a sodium        persulfate/sulfuric acid etch solution for 1 min. at room        temperature;    -   10. The through-holes of each panel are then rinsed with flowing        DI water for 1 min.;    -   11. The panels are then immersed into acidic Pre-Dip CIRCUPOSIT™        6520 for 0.5 min. at room temperature and then immersed into        CIRCUPOSIT™ 6530 Catalyst which is an ionic aqueous alkaline        palladium catalyst concentrate (available from Dow Electronic        Materials) for 1 min. at 40° C., wherein the catalyst is        buffered with sufficient amounts of sodium carbonate, sodium        hydroxide or nitric acid to achieve a catalyst pH of 9-9.5;    -   12. The through-holes of each panel are then rinsed with flowing        DI water for 1 min. at room temperature;    -   13. The panels are then immersed into a 0.6 g/L dimethylamine        borane and 5 g/L boric acid solution at 32° C. for 1 min. to        reduce the palladium ions to palladium metal;    -   14. The through-holes of each panel are then rinsed with flowing        DI water for 1 min.;    -   15. The panels are then immersed in the electroless copper        plating composition of Table 7 and copper is plated at 34° C.,        at a pH of 13 and copper is deposited on the walls of the        through-holes for 5 min.;    -   16. The copper plated panels are then rinsed with flowing tap        water for 4 min.;    -   17. Each copper plated panel is then dried with compressed air;        and    -   18. The walls of the through-holes of the panels are examined        for copper plating coverage using the backlight process        described below.

Each panel is cross-sectioned nearest to the centers of thethrough-holes as possible to expose the copper plated walls. Thecross-sections, no more than 3 mm thick from the center of thethrough-holes, are taken from each panel are placed under a conventionaloptical microscope of 50× magnification with a light source behind thesamples. The quality of the copper deposits are determined by the amountof light visible under the microscope that is transmitted through thesample. Inside the plated through-holes, transmitted light is onlyvisible in areas where there is incomplete electroless coverage. If nolight is transmitted and the section appears completely black, it israted a 5 on the backlight scale indicating complete copper coverage ofthe through-hole wall. If light passes through the entire sectionwithout any dark areas, this indicates that there is very little to nocopper metal deposition on the walls of the through-holes and thesection is rated 0. If sections have some dark regions as well as lightregions, they are rated between 0 and 5. A minimum of ten through-holesare inspected and rated for each board. Backlight values of 4.5 andgreater are indicative of commercially acceptable catalysts in theplating industry.

The average backlight value for each type of FR/4 glass epoxy panel isdisclosed in the table below.

TABLE 8 Panel Bath 25 Bath 26 370HR 4.8 4.4 EM825 4.8 4.6 IT-180 4.8 4.7NPGN 4.7 4.8 SY-1141 4.4 4.4 TU-662 4.6 4.7Overall both baths show very good backlight values.

What is claimed is:
 1. An electroless copper plating compositioncomprising one or more sources of copper ions, one or more pyridiniumcompounds, one or more complexing agents, one or more reducing agents,and, optionally, one or more pH adjusting agents, wherein a pH of theelectroless copper plating composition is greater than
 7. 2. Theelectroless copper plating composition of claim 1, wherein the one ormore pyridinium compounds or salts thereof are in amounts of at least0.5 ppm.
 3. The electroless copper plating composition of claim 1,wherein the one or more pyridinium compounds have a formula:

wherein R₁ is selected from the group consisting of linear or branched,substituted or unsubstituted (C₁-C₁₀)alkyl, substituted or unsubstituted(C₆-C₁₀)aryl, substituted or unsubstituted (C₆-C₁₀) heterocyclicaromatic group and substituted or unsubstituted benzyl; and R₂ isselected from the group consisting of hydrogen, hydroxyl, sulfate,amino, carbonyl, carboxyl, vinyl and amide.
 4. The electroless copperplating composition of claim 1, wherein the one or more complexingagents are chosen from sodium potassium tartrate, sodium tartrate,sodium salicylate, sodium salts of ethylenediamine tetraacetic acid,nitriloacetic acid and its alkali metal salts, gluconic acid,gluconates, triethanolamine, modified ethylene diamine tetraaceticacids, S,S-ethylene diamine disuccinic acid, hydantoin and hydantoinderivatives.
 5. The electroless copper plating composition of claim 1,wherein the one or more reducing agents are chosen from aldehydes,borohydrides, substituted borohydrides, boranes, saccharides, andhypophosphite.
 6. The electroless copper plating composition of claim 1,further comprising one or more compounds chosen from secondaryaccelerators, grain refiners and stabilizers.
 7. A method of electrolesscopper plating comprising: a) providing a substrate comprising adielectric; b) applying a catalyst to the substrate comprising thedielectric; c) applying an electroless copper plating composition to thesubstrate comprising the dielectric, wherein the electroless copperplating composition comprises one or more sources of copper ions, one ormore pyridinium compounds, one or more complexing agents, one or morereducing agents, and, optionally, one or more pH adjusting agents,wherein a pH of the electroless copper plating composition is greaterthan 7; and d) electroless plating copper on the substrate comprisingthe dielectric with the electroless copper plating composition.
 8. Themethod of claim 7, wherein the one or more pyridinium compounds or saltsthereof are in amounts of at least 0.5 ppm.
 9. The method of claim 7,wherein the electroless copper plating composition further comprises oneor more compounds chosen from stabilizers and secondary accelerators.10. The method of claim 7, wherein the electroless copper platingcomposition is at 40° C. or less.
 11. The method of claim 7, wherein thecatalyst is a palladium catalyst.